Apparatus for telephone trunk-lines.



PATENTED OCT. 13, 1903.

W. W. DEAN.

I APPARATUS FOR TELEPHONE TRUNK LINES.

1 APPLICATION FILED JAN. 14, 1902 N0 MODEL THE scams PETERS an, PkoTaLrn-u. wnsummom, a c.

UNrTED STATES IE atented October is, 1903..

PATENT Fries.

WILLIAM w. DEAN, OF oincAeo, inLiNois, ASSIGNOR TO WESTERN ELEC- rnro COMPANY, OF our-once, ILLINOIS, A CORPORATION or ILLINOIS.

APPARATUS FOR TELEPHONE TRUNK-LINES.

:IPECIFICATION forming part of Letters Patent No. 741,114, dated October 13, 1903.

Application filed January 14, 1902. Serial No. 89,656. (No mndeld To all whom it may concern.-

Be it known that 1, WILLIAM WV. DEAN, a citizen of the United States, residing at Ohicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Apparatus for Telephone Trunk-Lines, of which the following is a full, clear, concise, and exact description.

Myinven tion relates to trunk-lines for teleio phone-exchanges, and has for its object to provide improved apparatus and circuits whereby the answering operator who makes use of the trunk-line to extend a connection to a distant board may superviselthe connection and signal the called station directly from the answering-board without requiring the assistance or cooperation of the trunk operator at the receiving end of the line other than the mere insertion of the trunk-line plug into the springjack of the called line.

In modern telephone-exchanges in order that speech may be successfully transmitted between stations connected through a long trunk-line and for signaling purposes the trunk-line usually is not inade up of continuous conductors from one end to the other, but the end of the trunk-line at the receivingboard is separated from the main portion thereof by a repeating-coil, whereby the circuit is made continuous for alternating telephonic currents, but is divided or discontinuous as to direct currents. The receiving end of the trunk-line, which usually terminates in a calling-plug for insertion in the jack of 3 5 the called line, is usually provided with a battery bridged between the two halves of the winding of the repeating-coil connected with that end of the trunk-line for supplying current to Operate the microphone-transmitter at the called station. By interposing the repeating-coil in the trunk-line such battery isthus made local to the called line. Heretofore it has been usual for the operator at the receiving-board to signal the called station by means of a ringing-key associated with the calling-plug which forms the terminal of the incoming trunk, although it is highly desirable that the answering operator who supervises the connection should be enabled to signal the called station directly without the assistance of the trunk operator. Ringing cannot be successfully done from the answering-board through .the repeating-coil of the trunk-line for two reasons. First, the repeating-coil is constructed with great nicety to respond to highfrequency telephonic currents and will not work properly to transmit low-frequency alternating or pulsating currents, such as are used to ring the substation call bells, and, second, because pulsating 6o currents of a given polarity, as required to selectively signal the substations of partylines, cannot be transmitted through the repeating-coil. The coil actsto transform them into alternating currents. Again, if there is any bridge of the trunk-line between the call ing-key at the A board and the subscribers line the pulsating current applied to one limb'of the trunk-line for signaling a particular substation on the connected limb of the subscribers line will spread across this bridge to the other limb, thus ringing thebell on the other limb of the subscribers line.

In accordance with my invention the bridges of the trunk-line which contain the repeating coil and battery are normally out of the circuit and the limbs of the trunkline are normally continuous from the answering-board to the terminal plug at the receiving-board, so that a through-circuit for calling-currents is established from the answering-board clear to the substations of the line. The answering operator is thus enabled to signal the called station directly. Then when the called party answers the sig-. nal by removing his telephone from its switchhook an electrically-controlled switch at the receiving-board is automatically actuated, whereby the bridge circuit is connected across the trunk-line. The connection of the bridge-circuit across the trunk-line, while Y leaving a through-circuit,telephonically, in effect divides the trunk-line into two sections, one extending to the A board and the other to the subscribers line. The switch at the 5 1 receivingboard is preferably arranged to sever the trunk-line ahd introduce two bridges across the. circuit thereof, each of said bridges containing a winding of a repeating-coil. A battery for supplying the telephone-transmitter at the called station may be included in the bridge which is connected with the ends of the trunk-line leading to the calling-plug or trunk-line terminal at the receiving-board. The circuit of this battery is thus local to the called partys line, although the trunk-line is continuous with respect to alternating currents, the two sections thereof being united telephonically through the repeating-coil. The switch for controlling the connection of the bridge-circuit may be operated by an electromagnet controlled through the agency of a switch at the called station.

A further feature of my invention consists in improved apparatus and circuits for signaling between the two terminals of the trunk-line, whereby a signal for disconnection may be automatically displayed before the trunk operator when the answering operator removes the connection.

My invention is illustrated by the accompanying drawing, which is a diagram showing an ordinary telephone line extending from a substation to a central-office answering-switchboard and there connected in the usual manner with a trunk-line extending to a receiving-switchboard, the receiving end of the trunk-line being in turn connected with a party-line leading to four substation-s. The trunk-line is equipped with the apparatus and circuits of my invention.

The switchboard A is the answering-board, and the switchboard Bis the receiving-board. The attendantat the board Ais usually called the A operator, and the attendant at the board B is called the B operator. The trunk-line 75 extends in two limbs 1 2 from a spring-jack a at the answering-board to a terminal plug bat the receiving-board. The A operator is provided with the usual apparatus for connecting lines together, such apparatus consisting of a pair of plugs 0 (Z, united by link-conductors 3 4 of the plug-circuit.

- The plug-circuit is equipped with the usual supervisory signal apparatus, and the callingplug d is connected with four party-line ringing-keys d (l d 1 each of which is adapted when depressed to open the plug-circuit and connect one of the severed ends leading to the calling-plug with a source of calling-current of peculiar and distinctive character. Thus the key d connects the limb with the grounded source P of positive pulsating current, and key (1 connects the same limb 4 with another source N of negative pulsatingcurrent, while keys d and d connect the other limb 3 of the plug-circuit with the sources of current P and N, respectively.

The limb l of the trunk-line is connected whenno plug is in the jack a with the bat jack. The magnet of this relay is included in the local supervisory circuit of the callingplug d, said circuit being established in registering contacts of the plug and spring-jack and closed during the insertion of the plug.

Battery is thus cut off from the limb 1 of the trunk-line as long as the A operators plug (Z remains inserted in the trunk-jack.

At the B board the limbs 1 2 of the trunkline are connected to the armatures g g respectively, of the magnet g. The tips of the armatures g g are insulated from the main portions of said armatures and are connected, respectively, with the contact portions 1) b of the terminal plug 1). The armature g and its tip are normally connected together through the back contacts g 9 which are electrically united, and similarly the armature g and its tip are normally connected through the united contacts g 9 Both limbs of the trunk-line, therefore, are normally continuous from the spring-jack at the A board to the terminal plug at the B board. A repeating-coil is associated with the magnet g and is adapted to be introduced into the trunk-line circuit when the said magnet is excited and attracts its armatures. The front contacts g g of the armatures g 9 respectively, form the terminals of one winding 77/ of the repeating-coil, and similarly the front contacts g -g with which the separate tips of said armatu res engage, form the terminals of the other winding h of the repeating-coil. A battery t' is connected between the two halves of winding 71?, the pole of the battery nearest the contact g being grounded.

It will be seen that when magnet g is excited it will act to sever the trunk-line and introduce the windings of the repeating-coil into the circuit of the several ends thereof, the winding h being in circuit with the conductors 1 2, leading to the A board, and the winding k in circuit with the conductors 5 6, leading to the plug b. The helix of magnet g is included in a local circuit 7 from battery i, which is controlled by the relay is. The said relay is included in the conductor 6 of the trunk-line plng-circuit-and corresponds to the supervisory relay of an ordinary plugcircuit, being responsive to the flow of current in the line with which the plug may be connected. The local circuit7 of the magnet g is normally open at the contacts of the relay 70, but is closed when said relay is excited. The trunk-line plug is shown inserted in the spring-jack of an ordinary four-party telephone-line. The A operator may ring any one of the substation call-bells by depressing that one of the ringing-keys d d d d which corresponds to the station wanted, the bells at the substation being polarized to respond only to pulsating current flowing in a predetermined direction. Thus the bells at stations S and S respond to positive and negative pulsating currents, respectively, sent out over one limb of the line, while the bells at stations S and 8* respond to positive and negative currents, respectively, on the other limb of the line. Pulsating currents of the required sign can be transmitted from generators P and N at the A board over the trunk- ICC - the repeating-coil is not interposed in the circuit until the called subscriber answers. When he does, the taking of his telephone from its hook for use closes the circuit of the line in the usual way andpermits current to flow from battery 6 of the A operators plugcircuit through the relay is, whereby said re-v lay is excited. The relay 1c in drawing up its armature closes the local circuit 7, including magnet g, so that said magnet is excited by current from battery v) and draws 'up its armatures g g This severs the circuit of the trunk-line and introduces thewindings h' h of the repeating-coil, as before explained. The battery 1?, which is connected between the two halves of winding 11?, is thus bridged into the circuit of the called line for talking purposes. Current from this battery maintains the relay It in its excited condition, said relay being now cutoff from battery 6. Normally the circuit of battery 8 of the A operators plug-circuit extends from the A board through to the called substation but when the armatures g g are drawn npacircuit local to the trunk-line is established for this battery, said circuit being closed through the bridge which contains winding h of the repeating-coil. This circuit includes the supervisory relay associated with the A operators calling-plug, which relay thus becomes excited and shunts out its associated signal-lamp in the usual manner. Thus, although the tru nk-line is severed upon the response of the called subscriber, the

proper operation of the A operators supervisory signal apparatus is not interfered with, since signals from the called station which would affect it if the trunk-line werepermanently continuous are relayed back to it from the B board. When the conversation is finished, the replacing of the called-subscribers telephone upon its switch-hook interrupts the fiow of current through relay is, and thus brings about the restoration of the original through-circuit. Simultaneously with the denergization of the relay is at the B board the A operators supervisory relay is deprived of current, whereby the A operators supervisory lamp is lighted in the usual way to notify her that the connection may be removed.

I will now proceed to describe the system of signaling which I have invented whereby the B operator may be informed when the 'A operator removes the connection with the trunk-line at the A board in order that the said B operator may in turn free the trunkline from its connection at her end. A third contact piece or shank b is provided for the trunk-line plug b, said contact-piece being connected by a conductor 8 to the free pole of the grounded battery 11. Said conductor 8 includes serially a signal-lamp Z and a resistancecoil m. A relay n" is connected in a permanent shunt about the lamp Z; The testring of the spring-jack of the called line is l grounded, and whenthe trunk-plug is inserted in the jack a local circuit from battery 2' through the lamp Z, relay n, and resistance m is thus established in registering contacts of the plug and spring-jack. Normally the current from battery 2" in this local circult is so cut down by the resistance m that the lamp Z will not be lighted while said resistance remains in the circuit. The current, however, is at all times sufficient to energize relayn. A shunt-path for the current is provided about the resistance 0%, said shunt being normally open at the contacts of a relay 0. When the relay 0 is excited, it closes the shunt about the resistance m, so that the current in. the circuit 8 will be increased sufficiently to light the lamp. The magnet of relayo is of high resistance-say five thousand ohms-and the pole-piece thereof is provided with a heavy copper collar. The relay is thus rendered sluggish, so that it will not respond to alternating or pulsating currents, such as are used in ringing substation call-bells, although it will respond to direct current. This relay 0 is included in a grounded branch conductor 9, extending from the united back contacts g g of the relay g. The circuit of this conductor 9 is controlled by the relay n, which, it will be remembered, remains excited during the entire time that the trunk-plug is inserted in the jack of a called line. Since the branch 9, containing relay 0, is normally plained that the battery e of the A operatorsplug-circuit is connected with the conductor 1 of the trunk-line through the armature and back contact of the cut-0E relay f at the A board. When the A operator in response to a disconnect signal removes the calling-plug from the trunk-jack, the relay f will be deenergized, and battery e will thus be connected to the conductor 1 of the trunk-line, and so through conductor 9 with the relay 0'. The lamp Z therefore will-be automatically lighted at the B board upon the withdrawal of the A operators calling-plug from the trunk-jack. This constitutes a signal to the B operator to removethe trunk-plug from its connection, and when the signal is obeyed lampl and relay n will be deprived of. current. The armature of relay n in falling back breaksthe circuit 9 through relay 0.

I claim as my invention'' a 1. The combination of a telephone trunkline extending from an answering-switchboard to a receiving-switchhoard and connected at the last-mentioned board with a subscribers telephone-line, of means at the answering -'swi-tchboard for applying callingcurrent to the trunk-line, the conductors of said trunk-line being normally continuous, whereby the substation call-bell of the subscribers line may be rung directly from the answering switchboard, a repeatingcoil at the receiving-switchboard normally disconnected from the trunk-line, a magnet and switch-contacts operated thereby for severing the trunk-line and interposing the windings of said repeating-coil in the circuits of the severed ends thereof, and a circuit including a battery for exciting said magnet, said circuit being controlled through the agency of a switch at the subscribers station, substantially as set forth.

2. The combination with a telephone tr unkline extending from an answeringswitchboard to a receiving switchboard and connected at thelast-mentioned board to a subscribers line, of a repeating-coil at the receiving-switchboard normally disconnected from the trunk-line, means controlled in the use of the telephone at the substation of the subscribers line for interposing said repeating-coil in the trunk-line circuit, a source of current connected with the winding of the repeating-coil which is adapted to be connected in the circuit of the subscribers line, Whereby the telephone at the substation of the subscribers line may be supplied with current when the repeating-coil is interposed in the trunk-line circuit, a source of ringing-current and means for connecting the same with the trunk-line at the answering-switchboard, and switch contacts normally maintaining a through-circuit of the trunk-line independent of said repeating-coil, whereby ringing-current may be applied to the subscribers line directly from the answering switchboard, substantially as set forth.

3. The combination witha telephone trunkline extending from an answering-switchboard to a receiving-switchboard, of a terminal plug for the trunk-line at the receivingboard adapted for insertion in a subscribers telephone-line spring-jack, a local signal-circuit established by connection of the trunkline with the subscribers line, said circuitineluding serially a source of current, a resistance and a signal, a relay connected in the circuit, a shunt about said resistance, a second relay adapted to close the shunt about said resistance to permit an increased flow of current through the signal, and a circuit from the answering-board including a source of current together with the magnet-winding of said last-mentioned relay, said circuit being established at the receiving-board in switchcontacts. of said first-mentioned relay, and controlled by connection with the trunk'line at the answering-board, substantially as set forth.

4. The combination with a telephone trunkline extending between two switchboards, of means at one of the boards for connecting the trunk-line with a subscribers line, a source of calling-current and means at the other board for applying the same to the trunk-line, the trunk-line being normally continuous, whereby a substation of the subscribers line may be signaled directly from the distant board through the trunk-line, a repeating-coil normally disconnected from the trunk-line, and means controlled in the use of the telephone at the called station, for severing the trunk-line and connecting the severed ends telephonically through said repeating-coil,

substantially as described.

5. Thecombination withatelephone trunkline extending between two switchboards A B, of a subscribers line and a plurality of substation instruments connected therewith, means at the B switchboard for connecting the trunk-line with said subscribers line, means at the A switchboard for applying specialized calling-current to either limb of the trunkline, a bridge-circuit for the trunk-line at the B switchboard, a repeating-coil having windings included in said bridge-circuit, electrically controlled switch contacts controlling the connection of said bridge-circuit with the trunk line and normally maintaining the same disconnected therefrom, whereby a through-circuit for calling-currentis provided from the Aswitchboard over eitherlimb of the line to a called substation of the subscribers line, a switch at a called substation adapted to be operated in the use of the telephone apparatus, and means controlled through the agency of said switch for actuating said electrically-controlled switch-contacts at the B board, to connect the bridge-circuit across the trunk-line, substantially as set forth.

6. The combination withatelephonetrunkline extending between two switchboards A B, of a subscribers line and substation telephone apparatus, and means at the B switchboard for connecting the trunk-line therewith, a bridge-circuit for the trunk-line at the B switchboard, a repeating-coil having windings in said bridge-circuit, a battery in said bridge-circuit forsupplying current to the substation apparatus, switch -contacts controlling the connection of said bridge-circuit with the line and normally maintaining the same disconnected, whereby a through-circuit of minimum resistance is provided from the A switchboard to the substation, a switch at the substation, adapted to be operated in the use of the telephone apparatus, and means controlled through the agency of said switch for actuating the electrically controlled switch-contacts at the B switchboard, to connect said bridge-circuit with the trunk-line, substantially as set forth.

7. Thecombinationwithatelephonetrunkline extending between two switchboardsAB, of a subscribers line and substation telephoue apparatus and means at the B switchboard for connecting the trunk-line there with, a bridge-circuit for the trunk-line at the B switchboard, an induction-coil winding in said bridge-circuit, switch-contacts controlling said bridge-circuit and normally ICC disconnecting the same from the trunk-line, whereby a through-circuit is provided from the A switchboard to the substation of the subscribers line independent of said induction-coil winding, a switch at the substation adapted to be operated in the use of the telephone apparatus, and means controlled through the agency of said switch for connecting said bridge-circuit across the trunkline, substantially as set forth.

8. The combination with a telephone-circuit extending in a trunk-line from an A switchboard to a B switchboard, and thence by a subscribers line to a substation, of a source of current and a supervisory signal device included in the circuit at the A board, a switch at the substation for determining the flow of current in the circuit, a repeatingcoil and a grounded source of current '2: at the 13 board normally disconnected from the circuit, and means at the B board, controlled by the flow of current in the circuit, for conductivelysevering the circuit and inductively completing the same through said repeatingcoil, the ends thereof leading to the A board being directly united without any earth connection, and the ends leading to the substa tion being connected with said grounded source of current through a winding of said repeating-coil, substantially as set forth.

9. The combination'with a telephone trunkline and a snbscribers line united therewith at one end, of means for applying calling-current to the other end of the trunk-line, a repeating-coil adaptedto divide the trunk-line conductively, an electromagnetic switch normally completing a conductive circuit of the trunk-line independent of said repeatingcoil, but adapted when actuated to break said conductive circuit and substitute an inductive circuit through said repeating-coil, a switch at the subscribers station, and means controlled thereby for actuating said electromagnetic switch.

10. The combination with a telephone trunk line and a subscribers line united therewith at one end, of means for applying calling-current to the other end of the trunkline, an induction device adapted to divide the trunk-line conductively, an electromagnetic switch controlling a conductive extension of the trunk-line independent of the said induction device, and means for actuating said electromagnetic switch.

In witness whereof I hereunto subscribe my name this 23d day of July, A. D. 1900.

WILLIAM W. DEAN.

Witnessesr DE WITT O. TANNER, J. W. SKINKLE. 

